The use of external sensors in a restraint system for impact detection has been described in German Patent Publication No. 196 09 290.
Upfront sensors currently in use are acceleration sensors installed in the front deformation zone of the vehicle, i.e., on the radiator crossmember, which detect only in the longitudinal direction of the vehicle. It is possible for the acceleration sensors to be able to detect in the Y direction as well, for example for detecting the crash direction. The upfront sensors are basically used for improved detection of frontal problem crashes such as oblique impacts, truck underride crashes, and impacts on soft obstructions, for example, collisions with large animals such as moose, horses, or cattle.
In truck underride crashes, which carry a high risk of injuries and are centrally detectable much too late, and in which the upfront sensors are actually intended to enable timely deployment, it happens in currently used upfront sensors and sensor configurations, i.e., sensor systems, that the less mechanically stable radiator crossmember is bent upward or downward, depending on the height of the impact object, before the impact is detected. As used here, “impact object” refers to the rear part of a truck, i.e., the truck trailer underride protection, the truck trailer longitudinal chassis beam, the truck trailer hitch, or the bottom edge of the flatbed truck. The impact vehicle longitudinal chassis beams enter under these objects. This is why these crashes are so hazardous and are centrally detectable so late.
The upfront sensors which are sensitive only in the X direction are disoriented by the impact and, depending on the impact combination, are able to detect only a larger or smaller portion of the deceleration component in the X direction. Unfortunately, there have been several cases in truck underride crashes in which the occupant protection system did not deploy, or deployed too late, because of disoriented upfront sensors and the occupants were injured.